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Elk Creek Mine Subsidence <br />Page 5 <br />February 26, 2003 <br />• Group 3. The roughly 200-ft interburden thicknesses, shown on <br />Table 2, should be sufficient to eliminate any possibility of any <br />hydrologic collapse chimney connection between the underlying room <br />and pillar mine workings and the Elk Creek Mine (Piggott & Eynon, <br />1977). The stress concentrations above underlying barrier pillars <br />should be laterally distributed and, thereby, dissipated by the <br />thickness of the interburden and the high proportion of sandstone <br />in the interburden, roughly 60$ (Chanda, 1989). <br />An upper part of a landslide overlies the south side of <br />planned Panel #1 (Plate 2). This landslide was identified on the <br />Geologic Hazards Map for the North Fork of the Gunnison River by <br />the W.R. Junge (1978). The predicted maximum vertical subsidence <br />of the landslide, affected by mining Panel #1, will lower the top <br />of the landslide by roughly 7-ft. The lowering of the landslide <br />will decrease toward the south to zero, over a distance of <br />1,500-ft. Tilting the upper part of the landslide 0.27° <br />(16-minutes) back into the slope by mining Panel #1 must slightly <br />increase the current overall stability of the landslide mass. <br />• <br />'~ <br />Failure of the gateroad pillars between adjacent panels in the <br />panel groups will reduce individual panel surface subsidence <br />effects. This is true regardless of when the pillars fail, either <br />immediately after mining the second panel or long after completion <br />of the adjacent panels. Failure of the gateroad pillars will <br />decrease the downward deflection across the gateroad pillars. <br />Failure of the gateroad pillars should not affect subsidence <br />affects at the panel ends. <br />-5- <br />